Silica-alumina-chromium phosphate catalyst and hydrocarbon cracking therewith



SlLICA-ALUMINA-CEEOMIUM PHOSPHATE CATALYST AND HYDROCARBON CRACK- ING TMREWITH Alfred E. Hirschler, Springfield, and Edward J. Janoski,

Philadelphia, Pa., assignors to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey No Drawing. Application December 29, 1954 Serial No. 478,535

2 Claims. (Cl. 208-111) This invention relates to a catalytic composition effective in catalytic processes for converting hydrocarbons. More particularly, this invention relates to new and improved catalytic compositions, their preparation, and to a process for converting hydrocarbons employing the new catalyst wherein a specific hydrocarbon fraction, boiling above the gasoline range, is converted to gasoline of high octane rating.

The conversion of various petroleum hydrocarbon fractions by processes such as cracking, reforming, hydroforming, and the like, using a variety of catalysts and reaction conditions, has been described. Such heretofore described processes, however, are not suitable for converting the hydrocarbon fraction boiling substantially within the range of from about 375 F. to 500 F. to high octane gasoline in a single stage. Instead of achieving a good yield of high octane gasoline, there is produced gasoline hydrocarbons of relatively low octane rating usually in low yields, the production of normally gaseous hydrocarbons, such as propanes and butanes, is excessive, andthe reduction of catalyst activity is rapid. It has heretofore been necessary to employ at least two stages to convert a petroleum hydrocarbon fraction boiling above the gasoline range, especially a fraction boiling within the range of from about 375 F. to 500 F., to high octane gasoline. Such processes usually involve a cracking stage wherein a portion of the hydrocarbons are converted to hydrocarbons boiling in the gasoline range, and a reforming, or hydroforming, stage to upgrade the octane rating of the gasoline. In the upgrading stage, the use of two catalysts in separate reactors with a hydrocarbon separation step between the reactors, or the use of two catalysts in a single reactor, has heretofore commonly been required.

An object of this invention is to provide a new and improved catalytic composition effective for converting hydrocarbons.

Another object is to provide a process for converting a hydrocarbon fraction boiling within the range of from about 375 F. to 500 F. to high octane gasoline in a single stage and in good yield.

A still further object is to provide a process for the preparation of a new and improved catalyst.

Other objects and their achievement, in accordance with the invention will be apparent from the following specification.

General A new catalytic composition has been discovered which gives improved results in converting hydrocarbons. The new catalytic composition contains chromium phosphate, silica and alumina in defined quantities, as hereinafter discussed. It has been found that this new catalytic composition is especially efi'fective in converting relatively high boiling petroleum fractions, e.g., a fraction boiling within the range of from about 375 F. to 500 F., to gasoline hydrocarbons of high octane number, that the formation of normally gaseous hydrocarbons is substantially reduced as compared to heretofore described processes, and

" ited States atent that the normally gaseous hydrocarbons produced have a remarkably high olefinic content so that they are especially valuablein processes such as alkylation and polymerization.

The reactions involved in the process of the invention are primarily the cracking of the relatively high molecular weight hydrocarbons to hydrocarbons boiling in the gasoline range, and the dehydrogenation of hydrocarbons to produce hydrocarbons of higher octane number, such as the dehydrogenation of naphthenes to produce aromatic hydrocarbons. Hence, the process of the present invention is conveniently designated herein as dehydrocracking. Other reactions, however, are involved and assist in producing the high octane hydrocarbons prepared by the process, such as the isomerization of paraflins to produce more highly branched chain parafiins of relatively high octane number, and cyclization followed by dehydrogenation to produce aromatics from paraffins.

The new catalyst of the invention may be prepared by a variety of means, the general techniques of which are known in the art. However, a new method has been discovered which gives an especially effective catalyst. This new method of preparation is described hereinafter.

It is of primary importance that the limits on the ranges of components of the catalytic composition be observed as hereinafter discussed.

The catalyst As above stated, the catalytic composition of the present invention contains chromium phosphate, alumina and silica. it is important that the weight percent, based on the final composition, of each component be within the following ranges: chromium phosphate=0.5 to 10%, a-lumina=6 to 20% and silica=70 to 93.5% The values herein reported for chromium phosphate have been calculated for chromium orthophosphate (CrPo but it is realized that other compounds containing chromium, oxygen and phosphorus, such as chromium meta-phosphate, may be present. As used herein, chromium phosphate is intended, therefore, to include compounds containing chromium, oxygen and phosphorus.

When the quantity of chromium phosphate in the catalytic composition is below 0.5% by weight, a substantial loss of octane rating of the gasoline hydrocarbons and a decrease in the olefinic content of the normally gaseous hydrocarbons are observed, whereas in quantities above 10% by weight, excessive coke formation on the catalyst and excessive formation of normally gaseous hydrocarbons are observed. If the quantities of alumina or silica are varied from the stated ranges, the conversion of the high molecular weight hydrocarbons to hydrocarbons boiling in the gasoline range is adversely affected. Accordingly, it is of primary importance that the components of the catalytic composition be within the stated ranges.

Preparation of catalyst Although the catalytic composition of the present invention may be prepared by Various means, it is preferred to first prepare a synthetic silica-alumina composition, and to deposit the chromium phosphate thereon.

Synthetic silica-alumina compositions are well known as cracking catalysts, and heretofore described methods for their preparation may be employed in preparing the silica-alumina portion of the present catalyst. For ex ample, the silica-alumina portion of the catalyst may be prepared by impregnating silica with aluminum salts, by directly combining precipitated hydrated alumina and silica, or by joint precipitation of alumina and silica from aqueous solutions of their salts, and by washing, drying, and heating the resulting composition. The result I ing silica-alumina composition should have an activity index of at least 30, and preferably from 40 to 50. Activity index, as used herein, is a measure of the efliciency of a catalyst for cracking hydrocarbons and is determined by a method described by Alexander, Proceedings Am. Pet. Inst. 27 (III), 51 (November 1947).

Chromium phosphate is advantageously incorporated with the silica-alumina composition by impregnating the silica-alumina compositon with an aqueous solution containing an acid of phosphorus and a water soluble salt of chromium, such as ammonium dichromate. Orthophosphoric acid is the preferred acid of phosphorus. Any excess liquid is drained and the impregnated composition dried, such as by heating to from about 100 C. to 200 C., and calcined in contact with an oxidizing gas, such as air, at a temperature of from about 500 C. to 750 C. for from about minutes to 4 hours. excess'of the phosphate ion is present it should be removed by washing with water, preferably before calcining, and it is important that substantially no free phosphoric acid be present in the final composition.

The foregoing procedure, as has been found, yields a catalyst of exceptionally high activity in producing gasoline hydrocarbons at a high octane rating from higher boiling hydrocarbons.

Dehydrocracking The reactions involved in the present process for converting relatively high boiling petroleum hydrocarbons to gasoline hydrocarbons of high octane rating are primarily dehydrogenation and cracking, and hence the overall process-is conveniently designated as dehydrocracking. The gasoline product preferably contains only hydrocarbons having a molecular weight lower than the hydrocarbons of the charge stock, and hence includes only the hydrocarbons which have been cracked in the process.

As above stated, the newv catalytic composition of the invention is especially suitable for dehydrocracking hydrocarbon fractions boiling'in the range of from 375 F. to 500 F. to gasoline hydrocarbons of high octane rating, heretofore described processes and catalysts being unsuitable for this conversion. Accordingly, the use of the present catalyst will be described in terms of this preferred embodiment.

Especially suitable charge stocks are straight-run fractions having. anaphthene content of at least 10%, and preferably above 30%, say from about 30% to 75% by volume. Other fractions such as those obtained from catalytic cracking, and recycle gas oils in general, may be used.

In the process, temperatures within the range of from 450C. to 540 C. give good results and with the preferred hydrocarbon charge stock must be observed in order to obtain suitable conversion without excessive coke formation. The pressure is preferably maintained at about atmospheric pressure, but superatmospheric pressure up to about 100 p.s.i.g. can be used if desired. The space velocity must be maintained within the range of from about 0.5 to 3. It is preferred to employ a space velocity of, from 0.8 to 1.5 since within this range there'is obtained a high gasoline yield of high octane number. By space velocity, as used herein, is meant the liquid hourly. space velocity, which is the liquid volume of hydrocarbons charged per volume of catalyst per houna 1 In carrying out theprocess of the invention, it is preferred to pass the hydrocarbon charge through a bed of catalyst under the above conditions. By such operation theactivity of the catalyst is gradually decreased, principally due to the deposition of carbonaceous materials thereon. Periodic regeneration of the catalyst, such, as by discontinuing the operation, flushing the catalyst. bed with an inert gas such as steam, flue gas, nitrogen, or the like, and burning off the carbonaceous If an.

4 materials by passing an oxygen containing gas, such as air, through the hot catalyst-bed, is advantageously employed. Regeneration is generally advantageously employed at intervals of from-about 10 minutes to 2 hours, depending upon the particular operation and reaction vari'ablesx being used. it Hydrogen preferably is not employed in the process, but a small partial pressure thereof is not deleterious. In some other uses-of the present catalyst, however, an atmosphere of hydrogen is advantageous, especially where operation is at superatmospheric pressure, as hereinafter described.

Example In order to illustrates a preferred catalytic composition of the invention and its use in dehydrocracking, a catalytic composition, in accordance with the invention, was-prepared as follows, in which parts refers to parts by weight:

'397 parts of a synthetic silica-alumina composition containing about 19% water, prepared by coprecipitation andcontaining about 13% by weight alumina and having an activity index of about 46, was impregnated with an aqueous solution containing about 436 parts water, 29.6 parts of orthophosphoric acid and 32.26 parts of ammonium dichromate. A small amount of excess liquid was drained and the impregnated composition was dried by heating at a temperature of about C. for about 16 hours. The dried composition Was then calcined by heating for about 2 hours at a temperature of about650 C. in contact with air.

The resulting composition constitutes a preferred catalytic composition prepared in accordance with the invention and contained in percent by weight 8.8% chromium phosphate, 11.7% alur'ninaand 79.5% silica. i

In order to illustrate the efiicacy of this new catalytic composition for converting hydrocarbon fractions boiling in the range of 'frorn'375" F. to 500 F. to high octane gasoline hydrocarbons," a straight-run petroleum hydrocarbon fraction boiling in the range of from about 375 F. 'to 460 F., having an aromatic content of about 13% by volue and a naphthene content of about 50% by volume was contacted therewith. The following con ditions were employed during the contacting: temperature of cata1yst=504 0, space velocity=1.0, pressure=atmospheric. The catalyst bed was regenerated after operation for 20 minutes by burning carbonaceous materials therefrom with a stream of air as above described. Products were collected over 10 cycles of operation and regeneration. H p

A yield of gasoline hydrocarbons, i.e., hydrocarbons from pentane to those boiling at 350 F., of 21.8% by volume was obtained. There were also obtained 11.7% by volume of hydrocarbons having 4 carbon atoms, which contained 54.3 weight percent'olefins, principally isobutylene, and 1.66% by weight of hydrocarbonshaving 3 carbon atoms, which contained 80% propylene. The bottoms fraction, i.e., hydrocarbons boiling over 350 F, constituted 60.2% by volume of the charge. Where desired, a gasoline fraction having a higher end point can be separated from the reaction mixture thereby increasing" the observed yield of gasoline. However,it is preferred to maintain the boiling range of the gasoline product below the boiling range of the charge stock.

The gasoline fraction had an octane number of 99.1

(ASTM Method D908-53) and an aromatic content of 57% by volume.

If the above example is repeated, usingas the catalyst the silica-alumina composition on which was deposited chromium phosphate in the above example, the quantity of hydrocarbons having 4 carbon atoms is over 20% by volume of .which olefins constitute onlyabout 30.5% by The foregoing example illustrates a preferred embodiment of the invention, including a preferred catalytic composition and its preferred use in dehydrocracking a refractory, relatively high boiling hydrocarbon fraction to gasoline having a remarkably high octane number. The catalyst is also effective to dehydrocrack other relatively high boiling fractions, such as gas oils boiling from about 400 F. to 750 F. or higher, to gasoline.

When other catalytic compositions within the scope of the present invention are employed, substantially equivalent results are obtained, and when other operating conditions are employed Within the ranges herein described, substantially equivalent results are obtained. The process may also be operated batchwise or as a moving bed or fluidized process by maintaining the reaction conditions equivalent to those herein described.

The catalyst of the invention can be used in other reactions involving the conversion of hydrocarbons, such as destructive hydrogenation using elevated pressures in an atmosphere of hydrogen, reforming, and the like, in which catalytic conversion conditions known to be effective in such processes give good results.

The invention claimed is:

1. A catalyst for use in the conversion of hydrocarbons consisting essentially of a synthetic silica-alumina composition having a cracking activity index of at least impregnated with from 0.5 to 10% by weight, based on the final composition, of chromium phosphate, wherein the quantity of silica is from to 93.5% by weight, based on the final composition, and the quantity of alumina is from 6 to 20% based on the final composition.

2. Process of cracking which comprises contacting a petroleum fraction boiling in the range of from 375 F. to 500 F. with a catalyst consisting essentially of, in percent by weight, 70 to 93.5% silica, 6 to 20% alumina and 0.5 to 10% chromium phosphate the silica-alumina component of the catalyst having a cracking activity index of at least 30 at a temperature within the range of from 450 C. to 540 C., a space velocity of from 0.5 to 3 and a pressure of about atmospheric, and recovering gasoline of high octane rating from the reaction mixture.

References Cited in the file of this patent UNITED STATES PATENTS 1,812,398 Galle et al June 30, 1931 2,331,338 Michael et al Oct. 12, 1945 2,647,860 Plank et a1. Aug. 4, 1953 

1.
 2. PROCESS OF CRACKING WHICH COMPRISES CONTACTING A PETROLEUM FRACTION BOILING IN THE RANGE OF FROM 375*F. TO 500*F. WITH A CATYST CONSISTING ESSENTIALLY OF, IN PERCENT BY WEIGHT, 70 TO 93.5% SILICA, 6 TO 20% ALUMINA AND 0.5 TO 10% CHROMIUM PHOSPHATE THE SILICA-ALUMINA COMPONENT OF THE CATALYST HAVING A CRACKING ACTIVITY INDEX OF AT LEAST 30 AT A TEMPERATURE WITHIN THE RANGE OF FROM 450*C. TO 540*C., A SPACE VELOCITY OF FROM 0.5 TO 3 AND A PARESSURE OF ABOUT ATMOSPHERIC, AND RECOVERING GASOLINE OF HIGH OCTANE RATING FROM THE REACTION MIXTURE. 